Sealing means for axial flow compressor discharge



y 4, 1968 c. c. MOORE 3,383,033

SEALING MEANS FOR AXIAL FLOW COMPRESSOR DISCHARGE Filed April 2'7, 19663 Sheets-Sheet l a a E 'El E.

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INVENTOR. (l/fl ffl/l/ I, A/flflff C. C. MOORE May 14, 1968 SEALINGMEANS FOR AXIAL FLOW COMPRESSOR DISCHARGE 3 Sheets-Sheet 2 Filed April27, 1966 y 4, 1968 c. c. MOORE 3,333,033

SEALING MEANS FOR AXIAL FLOW COMPRESSOR DISCHARGE Filed April 27, 1966 3Sheets-Sheet 5 United States Patent 3,383,033 SEALING MEANS FOR AXIALFLOW COMPRESSOR DISCHARGE Clinton C. Moore, Cincinnati, Ohio, assignorto General Electric Company, a corporation of New York Filed Apr. 27,1966, Ser. No. 545,611 12 Claims. (Cl. 230-132) ABSTRACT OF THEDISCLOSURE The invention concerns an axial flow compressor having arotor, an outer casing forming an annular flow path for pressurizedgases, an inner frame forming with the outer casing a continuation ofthe flow path, and fluid biased axially movable seal means between theframe and the rotor.

The present invention relates to improvements in axial flow compressorsand more particularly to improvements in providing improved sealingmeans between the usual rotor thereof and adjacent stationary framemembers at the discharge of the compressor.

A compressor rotor defines the inner surface of an annular flow pathwhich is defined by a relatively stationary frame member in directingthe presurized air to a point of ultimate use. The amount of air lost atthe juncture of the rotor and frame member is an important factor to theefficiency of axial flow compressors.

The importance of high compressor efiiciencies is perhaps bestexemplified by their use in gas turbine engines. In such engines anaxial flow compressor provides pressurized air to maintain combustionand provide a hot gas stream of a high energy level which may bedischarged through a nozzle to provide a propulsive force or may drive aturbine which provides a rotative power output. Particularly in thepropulsion of aircraft it is essential that the overall engine operateat a high efficiency level in order that the full advantages of the gasturbine engine may be realized. Loss of air from the compressor thusdetracts not only from the efiiciency of the compressor itself but alsothe overall eficiency of operation of the engine.

The object of the invention is, therefore, to provide an improved,reliable, highly effective, and economical seal between the rotor of anaxial flow compressor and the adjacent frame member which define a flowpath for the pressurized air discharged from the compressor.

In the recited environment of an axial flow compressor these ends areattained through the use of sealing means characterized by the provisionof an axially movable ring member adjacent the rear end of thecompressor rotor. Primary sealing means are formed on the ring and rotorand comprise a radial sealing surface and an annular tooth projectingtheretowards which coact to prevent leakage of pressurized air. Airbearing means spaced radially inwardly from the primary sealing meansare also formed by cooperative portions of the ring member and rotor.The air bearing means are effective when the ring member and rotor arein close proximity to maintain an accurate, closely spaced rleation ofthe primary sealing means, whereby the sealing means are highlyeffective. The ring member, the compressor rotor, and the adjacent frameform an annular chamber opening into the flow path for pressurized airdischarged from the compressor. The radial area of the ring member whichis exposed to this chamber is sufficiently great to provide a yieldableforce which displaces the ring member into close proximity with thecompressor rotor when the pressure of the air discharged from thecompressor reaches ice ing means to thus maintain a highly effectiveseal at the juncture of the inner frame and rotor.

In normal operation there is no contact between the stationary androtating elements and thus essentially no wear. Further means areprovided for urging the ring member to an axially retracted positionwhen the discharge pressure of the compressor falls below a given level.The air bearing and air pressure force which displaces the ring providefor effective sealing action in spite of variations in the axialposition of the compressor rotor.

It is also preferable to vent the area between the primary sealing meansand the air bearing to a substantially lower pressure, usuallyatmospheric, in order to obtain greater effectiveness of the airbearing.

Further, it is preferred that secondary. sealing means he formed on thering member and rotor and comprise a cylindrical surface; and a toothprojecting radially theretowards. Thus at relatively low compressordischarge pressures, or Where the primary sealing means is for somereason inoperative, delivery of pressurized air Will be maintainedalbeit at a reduced level.

It is also preferable that the ring member be configured such that thesummation of torque forces about the center of gravity of thelongitudinal half section thereof, resulting from pressurization of theannular chamber which is defined thereby, be substantially zero. Thusany tendency to twist the ring member is minimized, if not eliminated,and the effectiveness of the primary sealing means is maintained at ahigh level over a wide range of compressor discharge pressures.

The above and other related objects and features of the invention willbe apparent from a reading of the following description of thedisclosure found in the accompanying drawings and the novelty thereofpointed out in the appended claims.

In the drawings:

FIGURE 1 is a diagrammatic view of a gas turbine engine having an axialflow compressor and sealing means therefor which embody the presentinvention;

FIGURE 2 is an enlarged longitudinal section of the discharge portion ofthe axial flow compressor seen in FIGURE 1, under a condition ofrelatively high discharge pressure;

FIGURE 3 is a section similar to FIGURE 2 illustrating a condition ofrelatively low compressor discharge pressure;

FIGURE 4 is a section taken on line IVIV in FIGURE 3; and

FIGURE 5 is a longitudinal section through the discharge portion of anaxial flow compressor illustrating sealing means embodying an alternateembodiment of the invention.

FIGURE 1 schematically shows a gas turbine engine 10 in which thepresent invention finds particular utility. The engine 10 comprises acompressor 12, a combustor 14, a turbine 16, and a discharge nozzle 18.The compressor 12 includes a rotor 20 having a plurality of blades 22arranged in stages along its length and cooperating with stator blades24 extending inwardly from an outer casing 28, thereby forming an axialflow compressor for delivering pressurized air to support combustion inthe combustor 14. The hot gas stream thus generated drives the turbine16 to derive power for rotating the compressor rotor 20, being connectedthereto by a hollow shaft 30. After passing through the turbine 16, thehot gas stream may be discharged through the nozzle 18 to provide apropulsive force in the operation of aircraft.

It will be apparent that the compressor casing 28, in combination withthe rotor 20, defines an annular flow path leading to the combustor 14.This annular flow path, beyond the compressor 12, is defined by anextension of the casing 28 and a frame member 32 which is generallyaligned with the rear end of the rotor 20. One of the serious problemsin attaining high efficiency in the operation of gas turbine engines isto minimize loss of pressurized air discharged from the compressor atthis juncture between the rapidly rotating compressor rotor and thestationary frame member 32.

The rear end of the compressor rotor 20 (FIGURES 24) comprises a disc 34to which is secured an annular sealing plate 36 means of bolts 38. Thestationary frame 32 is compositely formed by a frame member 40 which hasa lip 42 substantially aligned with the outer circumference of the rearend of the rotor 20 and is closely spaced therefrom to provide a smoothflow path for pressurized air discharged from the compressor. Bolts 44join this compositely formed frame structure.

A ring member or seal body 46 is guided for movement toward and awayfrom the rotor 20 by cooperating flanges 48 and 50. A circumferentiallabyrinth sealing tooth 52 projects from the ring member 46 towards thesealing plate 36. The ring member 46 is also provided with a radialflange 54 which terminates in a labyrinth sealing tooth 56. A flange 58projects from the sealing plate 36 and overlies the tooth 56 in allpositions of the ring member 46.

The rotor 20, the ring member 46, and the frame member 40 define anannular chamber 60 which opens into the flow path of air discharged fromthe compressor 12, and therefore, the chamber 60 is pressurized tosubstantially the same value as the compressor discharge pressure. Asplit ring 62 provides a seal for the chamber 60 between the axiallymovable ring member 46 and the frame member 40, being maintained insealing engagement therewith by pressurization of chamber 60. It will benoted that the contact area of ring 62 engaging the frame 40 and ringmember 46 is relatively small in order to minimize frictional drag onthe latter as it is displaced toward and away from the rotor 20, aslater described.

In normal compressor operation a highly effective compressor dischargeseal is provided by the labyrinth tooth 52 which is closely spaced fromthe plate 36, in the order of .001 inch. A force derived from thecompressor discharge air yieldingly urges the ring member 46 towards thesealing plate 36 and the close spacing of the labyrinth sealing tooth 52is maintained by an air bearing 63 between the ring member 46 and plate36. The ring member 46 thus can float and accommodate, Within limits,variations in the axial position of the compressor rotor 20,

Expansible chamber means are shown in FIGURES 2-4 for obtaining theforce urging the ring member toward the plate 36. These expansiblechamber means comprise a plurality of pistons 64 which are slidableaxially in the ring member 46 with their outer ends bearing against theframe member 40. Passageways 66 lead from the annular chamber 60 tochambers 68 in which the pistons 44 are slidable. The pistons areprovided with radial holes 70 so that pressurized air leakingtherethrough will minimize friction to facilitate displacement of thering member 46.

The air bearing 63 is preferably externally pressurized by the provisionof passageways 72 which direct pressurized air from the chambers 68between the opposed surfaces of the ring member 46 and sealing plate 36which comprise the air bearing. It is also preferable that the areabetween the air bearing and the labyrinth sealing tooth 52 be vented toa lower pressure, usually atmospheric, for most effective air bearingoperation. To this end a counter bored clearance hole 74 opens into thearea between the air bearing and the sealing tooth 52 so that air fromthis area may be vented through the ring member 46 and then throughholes 76 in the frame 40 to the opposite side thereof which is atatmospheric pressure or substantially so.

The y'ieldable force provided by the pistons 64, in combination with thedescribed air bearing, maintains the desired spacing of the labyrinthsealing tooth 52 and a highly effective sealing action regardless of anyvariations in the axial position of the compressor rotor 20.

The present seal has the further benefit of being highly effective overa wide range of compressor discharge pressures. This results from thefact that there is no substan tial twisting moment on the ring member.More specifically there is no twisting moment on the illustrated,longitudinal half section of the ring member. Thus, it will be evidentthat the effective force vector F of the air bearing 63 and theeffective force vector F of the expansible chambers on the ring memberare equal and opposite, with no resultant twisting or torque force onthe ring member. Further, the radially inward force exerted on the outersurface of the ring member 46 which defines the chamber 60 isdistributed from the tooth 52 to the point of engagement of the sealingring 62 therewith. The effective radial force vector F passes throughthe center of gravity cg of the ring member 46 so that there is noresultant twisting force therefrom. The air pressure forces on oppositesides of the flange 54 are equal and opposite and consequently there isno resultant effective force vector in an axial direction.

The described air pressure forces are the only forces of significancewhich could tend to deform the ring member 46 by twisting and result ina change in the orientation of the end face of the tooth 52 relative tothe sealing plate 36. Thus, the end face of the tooth 52 may beaccurately machined to provide an effective sealing action over the fullrange of compressor discharge pressures.

At low rates of rotation of the compressor rotor 20 sufficient airpressure may not be available for effective operation of the airbearing. To prevent contact between the ring member 46 and the rotor 20,means are provided for yieldingly urging the ring member in spacedrelation therefrom. These means comprise a plurality of springs 78 whichare coiled about bolts 80. The outer set of bolts 80 extend through thecounter bored clearance holes 74, pass through the frame 40, and havenuts 82 threaded thereon to adjust the force exerted by the springs 78on the ring member 46. The inner set of bolts 80 similarly pass throughthe ring member 46 and frame 40 and are likewise provided with adjustingnuts 82. When the compressor discharge pressure falls below a givenlevel the springs 78 displace the ring member 46 to the retractedposition shown in FIGURE 3.

When operation of the engine 10' is initiated, the ring member 46 ismaintained in spaced relation from the rotor 20 by the springs 78. Ascompressor discharge pressure builds up there is a pressure increase inthe annular chamber 60 due to the sealing action of the tooth 56. Thisdevelops a pressure differential on opposite sides of the flange 54 witha resultant force tending to displace the ring member to its operativeposition contiguous with the sealing plate 36. Simultaneously there is apressure increase in the chambers 68 which also tends to develop a forcedisplacing the ring member to its operative position wherein the tooth52 becomes the primary sealing means, as above described.

If for some reason the air bearing should fail to maintain the ringmember 46 in spaced relation from the plate 36, it is desired thatdamage be maintained at a minimum and preferably that no damage occur toany of the rotating parts. Thus, the portion of the ring member 46 whichforms a part of the air bearing 63 is surfaced with a layer 84 ofsacrificial material, such as a low melting point metal alloy. In theevent of air bearing failure the sacrificial layer 84 will be melted byfriction without injury to the plate 36. The tooth 52 being a relativelythin section will also burn or melt away without injury to the plate 36.It will be noted that the coils of springs 78 are arranged so that theirsolid heights will serve as a positive limit to displacement of the ringmember 46 towards the rotor 20 so that engagement of the substrate towhich the layer 84 is bonded with the plate 36 is prevented.

In the event of such a malfunction, excessive leakage of compressordischarge air is prevented by the labyrinth tooth 56 which thusfunctions as a secondary sealing means. Operation of the engine 10 ismaintained as a sufficient volume of air continues to be delivered tothe combustor 14 for generating a hot gas stream, albeit at a reducedenergy level.

FIGURE illustrates an alternate embodiment of the invention wherein adifferent form of ring member 46' is provided with a primary sealingtooth 52 which is arranged to cooperate with the sealing plate 36 whichis mounted on the compressor 20, as before described. The ring member 46likewise has a secondary sealing tooth 56, projecting from a radialflange 54 which cooperaates with the sealing plate flange 58.

The annular chamber 60 is again defined by the rotor 20, a modifiedframe member 40, and the ring member 46'. This chamber is furtherprovided with a sealing ring 62 which seals the chamber 60 at thejuncture of the frame 40 and ring member 46' while permitting the ringmember 46' to be displaced toward and away from the compressor rotor 20.The sealing ring 62 is again relieved so that frictional forces areminimized to facilitate such displacement of the ring member 46'. Agarter spring 83 and a plurality of compression springs 85 are providedto insure effective sealing by the split ring 62' when the pressure inchamber 60 is relatively low.

Passageways 86 extend from the chamber 60 to passageways 88 which directpressurized air between the opposed surfaces of the ring member 46' andsealing plate 36 to provide an air hearing, as before, which accuratelyspaces the sealing tooth 52 from the sealing plate 36 and thus maintainsa highly efficient sealing action. Angularly spaced passageways 90 ventthe area between the air bearing 63 and the sealing tooth 52 toatmosphere for optimum sealing operation.

The primary difference in the present embodiment is that the expansiblechamber means have been eliminated in utilizing the compressor dischargepressure to yieldably maintain the ring member in a position where theair hearing accurately positions it. T 0 this end the ring member 46 isconfigured so that there is a pressure differential on opposite sides ofthe radial flange 54' due to the location of the primary sealing tooth52. Thus there is provided a resultant effective force F which displacesand yieldably maintains the ring member 46 in its operative positionwherein the sealing tooth 52 is closely spaced from the plate 36.

In this alternate embodiment provision is also made to prevent anysubstantial twisting of the ring member which would tend to reduce theeffectiveness of the sealing action particularly over a wide range ofcompressor discharge pressures. This end is similarly achieved by abalance of the effective air pressure forces on the longitudinal halfsection of the ring member 46' as illustrated in FIGURE 5. The axialforce vector F produces a counterclockwise turning moment about thecenter of gravity C.G., on this longitudinal half section. The effectiveforce vector F of the air bearing likewise produces a counterclockwisetorque about the center of gravity. These counterclockwise torque forceare balanced by equal torque force provided by the effective forcevector F resulting from the radially inward air pressure force on theouter surface of the ring member. The net result is that there is notwisting moment from these air pressure forces about the center ofgravity of the longitudinal half section. To repeat, this balance oftorque forces enables effective sealing action to be maintained.

As in the previous embodiment, means are provided for retracking thering member 46 from the compressor rotor 20 when compressor dischargepressure falls below a given value. Thus studs 92 project through theframe member 40' and have springs 94 coiled there-abouts and confined bynuts 96 so that there will be no contact between the ring member 46 andthe rotor 20 at low pressure levels.

Other modifications will occur to those skilled in the art and the scopeof the present invention is therefore to be derived solely from thefollowing claims.

Having thus described the invention, what is claimed as novel anddesired to be secured by Letters Patent of the United States is:

1. In an axial flow compressor having a rotor and an outer casingforming an annular flow path for pressurized gas to be dischargedtherefrom, an inner stationary frame aligned with and adjacent thedischage end of said rotor and forming, in combination with said casing,a continuation of said flow path,

sealing means for preventing, or at least minimizing,

the loss of highly pressurized air at the juncture of said inner frameand said rotor, said sealing means comprising, an axially movable ringmember, primary sealing means respectively formed on said ring and rotorand comprising a radial sealing surface and an annular tooth projectingtowards said surface,

air bearing means spaced radially inwardly from said primary sealingmeans and formed by cooperative portion on said rotor and said ringmember, said air bearing means being effective when said ring and rotorare in close proximity to maintain an accurate, closely spaced relationof said primary sealing means,

means urging said ring member to an axially retracted position to saidrotor when the discharge pressure of the compressor falls below a givenlevel,

said rotor, said ring member, and said inner frame forming an annularchamber opening into the flow path for pressurized air discharged fromsaid compressor,

the radial area of said ring member exposed to said chamber beingsuificiently great that a force is provided for displacing said ringmember into said close proximity with said rotor upon the pressure ofair discharged from said compressor reaching a given value whereby theair bearing means may accurately control the spacing between said toothand said radial sealing surface and thus maintain a highly effectiveseal at the juncture of the inner frame and rotor.

2. Sealing means as in claim 1 wherein,

the air bearing means is externally pressurized by way of passagewaysextending thereto through said ring, from said chamber.

3. Sealing means as in claim 2 wherein,

means are provided for venting the area between said air bearing andsaid primary sealing means to a substantially lower pressure.

4. Sealing means as in claim 1 wherein,

secondary sealing means are respectively formed on said ring member androtor and comprise a cylindrical surface and a tooth projecting radiallytowards said surface, the axial extent of said cylindrical surface beingsuflicient to form a seal with said radially projecting tooth throughoutthe range of axial movement of the ring member.

5. Sealing means as in claim 1 wherein,

expansible chamber means are provided between said ring and said frameand passageway means connect said expansible chamber means with saidannular chamber whereby said expansible chamber means is pressurized byair discharged from the compressor to provide the force which iseffective to displace said ring to its position wherein the air bearingmeans accurately positions the primary sealing means.

6. Sealing means as in claim 2 wherein,

the ring member has a plurality of axially disposed pistons slidabletherein and angularly spaced from one another around the ring member,the outer ends of said pistons engaging said frame member and the innerends of said pistons defining expansible chambers,

passageway means connect said expansible chambers with said annularchamber, whereby pressurization of said annular chamber and theexpansible chambers will provide the force for displacing said ringmember into close proximity with said rotor to render the air bearingeffective in maintaining the desired spacing of the primary sealingmeans, and further wherein,

passageway means extend from said expansible chambers to said airbearing to provide external pressurization thereof from said annularchamber.

7. Sealing means as in claim 6 wherein the inner ends of said pistonsare hollow and said pistons have radial passageways extendingtherethrough to provide an air film which minimizes friction between thepistons and the ring member.

8. Sealing means as in claim 6 wherein,

said ring member has a flange extending radially outwardly therefrominto said annular chamber and terminates in a labyrinth tooth,

said rotor has a flange projecting into overlying relation with saidradial flange to provide in cooperation with the tooth thereon asecondary sealing means,

the opposite sides of said radial flange having essentially the samearea so that there is no resultant effective force in an axial directionresulting from pressurization of said annular chamber,

considered in longitudinal half section, the effective force vector ofthe air bearing on said ring member is essentially aligned with the axesof said pistons,

the ring member is configured so that the radially inwardly effectiveforce vector on its outer surface defining aid annular chamber passesessentially through the center of gravity of the half section,

whereby the eflectiveness of the primary sealing means is maintained ata high level over a wide range of compressor discharge pressures.

9. Sealing means as in claim 8 wherein,

the means for urging said ring member to an axially retracted positioncomprise a plurality of compression springs which are compressed as thering member is displaced towards said rotor,

the annular tooth of the primary sealing means is formed on said ringmember,

the portion of the air bearing means formed on said ring member issurfaced with a layer of sacrifical material bonded thereto and,

the solid height of the compression springs serves as a limit todisplacement of the ring member towards said rotor and prevents contactbetween the rotor and the substrate to which said sacrificial layer issaid bonded in the event of a failure of said air bearing means.

10. Sealing means as in claim 1 wherein,

one of the cooperative portions of said ring member and rotor formingsaid air bearing means is surfaced with a layer of sacrificial materialbonded thereto and means are provided for limiting displacement of thering member towards said rotor and preventing contact therebetween withthe substrate to which the sacrificial layer is bonded.

11. Sealing means as in claim 3 wherein,

the ring member is configurated such that there is no substantialturning moment about the center of gravity of its longitudinal halfsection resulting from air pressure force-s thereon.

12. Sealing means as in claim 3 wherein,

the ring member has a flange extending radially outwardly therefrom intosaid annular chamber and terminates in a labyrinth tooth,

said rotor has a flange projecting into overlying relation with saidradial flange to provide in cooperation with the tooth thereon asecondary sealing means,

the tooth of the primary sealing means i formed on said ring member andprojects from said flange and defines the base of said radial flange,the side of said flange towards said rotor having a lesser area than theopposite side whereby pressurization of said annular chamber results inan effective force which displaces said ring member toward said rotor torender the air bearing means effective to position the pimary sealingmeans,

the effective force vector on said radial flange and the eflective forcevector of the air bearing means on said ring member producing a torqueon the longitudinal half section of the ring member in one directionrelative to its center of gravity,

ring member being configured such that the radial force vector thereonresulting from pressurization of said annular chamber produces a torquethereon relative to its center of gravity which balances the torqueresulting from said other effective force vectors, whereby there is noresultant twisting moment on the longitudinal half section relative toits center of gravity.

References Cited UNITED STATES PATENTS EVERETI'E A. POWELL, 1a., PrimaryExaminer.

